Fabrication of high-entropy alloy wire and multi-principal element alloy wire

ABSTRACT

In various embodiments, metallic wires are fabricated by combining one or more powders of substantially spherical metal particles with one or more powders of non-spherical particles within one or more optional metallic tubes. The metal elements within the powders (and the one or more tubes, if present) collectively define a high entropy alloy of five or more metallic elements or a multi-principal element alloy of four or more metallic elements.

RELATED APPLICATION

This application claims the benefit of and priority to U.S. ProvisionalPatent Application No. 62/287,690, filed Jan. 27, 2016, the entiredisclosure of which is hereby incorporated herein by reference.

TECHNICAL FIELD

In various embodiments, the present invention relates to the formationand processing of wires composed of high-entropy alloys and/ormulti-principal element alloys.

BACKGROUND

High-entropy alloys (HEAs) are typically defined as alloys containing 5or more constituent elements each with a concentration between 5 and 35atomic %. The defining feature of HEAs over other complex alloys isthat, due to their high entropy of mixing, they essentially consist of asimple solid solution phase, rather than forming one or moreintermetallic phases. Various HEAs exhibit one or more superiormechanical properties such as yield strength, fracture toughness, andfatigue resistance. Multi-principal element alloys (MPEAs) are similarto HEAs but may include as few as four constituent elements. However,many HEAs and MPEAs, particularly those that include one or morerefractory metals (e.g., Nb, Mo, etc.) are quite difficult to fabricateand utilize due to their high strength and limited ductility. Becausediffusion tends to be quite slow in HEAs and MPEAs, bulk quantities ofthese materials are also often quite difficult to homogenize. These andsimilar issues have limited the widespread adoption of many HEAs andMPEAs.

Additive manufacturing, or three-dimensional (3D) printing, is a widelyutilized technique for rapid manufacturing and rapid prototyping. Ingeneral, additive manufacturing entails the layer-by-layer deposition ofmaterial by computer control to form a three-dimensional object. Mostadditive manufacturing techniques to date have utilized polymeric orplastic materials as raw materials, as such materials are easily handledand melt at low temperatures. Since additive manufacturing involves themelting of only small amounts of material at a time, the process has thepotential to be a useful technique for the fabrication of large, complexstructures composed of HEAs or MPEAs. Specifically, the small melt poolof material utilized at any point in time during an additivemanufacturing process may result in small molten volumes ofsubstantially homogenous alloy material that cool at a rate sufficientto stabilize the homogenized composition of the alloy. That is, thesmall size of the melt pool should promote mixing of the alloyconstituents, and the high cooling rate should limit segregation,promoting formation of a substantially homogeneous alloy.

Unfortunately, additive manufacturing of metallic materials is notwithout its challenges. When metallic precursor materials for additivemanufacturing possess significant amounts of oxygen or other volatilespecies (e.g., calcium, sodium, antimony, phosphorus, sulfur, etc.), themelting of such materials may result in sparking, blistering, andsplattering (i.e., ejection of small pieces of the materialsthemselves). In addition, even if a three-dimensional part is fabricatedutilizing such materials, the part may exhibit excessive porosity,cracking, material splatter, and insufficient density and machinability.

In view of the foregoing, there is a need for improved precursormaterials for the additive manufacturing of metallic parts, and inparticular parts composed of HEAs and MPEAs.

SUMMARY

In accordance with various embodiments of the present invention, wiresfor use as feedstock for additive manufacturing processes of HEAs orMPEAs are fabricated from powders of the various constituent elements ofthe alloy. The powders are formed utilizing one or more techniques thatminimize or substantially reduce the amount of oxygen and other volatileelements within the powders. In this manner, the amount of such volatilespecies within the wire is minimized or reduced. For example, variouspowders may be formed and/or treated via a hydride/dehydride process,plasma densification, and/or plasma atomization, and the powders mayhave low concentrations of volatile species such as oxygen (e.g., oxygencontents lower than 300 ppm, or even lower than 100 ppm). Variouspowders or powder precursors may even be combined with one or morematerials (e.g., metals) having a higher affinity for oxygen (e.g.,calcium, magnesium, etc.), deoxidized at high temperature, and thenseparated from the high-oxygen-affinity material via, e.g., chemicalleaching, as detailed in U.S. Pat. No. 6,261,337, filed on Aug. 19, 1999(the '337 patent), the entire disclosure of which is incorporated byreference herein.

In addition, various embodiments of the present invention feature HEA orMPEA feedstock wire fabricated using powders of the alloy's constituentelements (or binary or ternary mixtures or alloys thereof) that havedifferent particle sizes and/or volumetric shapes (or morphologies) inorder to minimize the amount of inter-particle space within the wire.Since such space may include or trap oxygen or other volatile specieswithin the wire, minimization of the space typically results in thesubstantial reduction of such species within the wire. Such wire maysubsequently be melted (via, e.g., application of an electron beam or alaser) to fabricate a three-dimensional part utilizing anadditive-manufacturing technique. For example, in various embodiments ofthe present invention, tungsten and/or molybdenum powders are plasmadensified and thus are composed of substantially spherical particles.Such powders are mixed with multiple other powders formed utilizinghydride/dehydride processes to form one or more HEAs or one or moreMPEAs. As known in the art, hydride/dehydride processes involve theembrittlement of a metal via hydrogen introduction (thereby forming ahydride phase), followed by mechanical grinding (e.g., ball milling) anddehydrogenation (e.g., heating in a vacuum); the resulting particlestend to be highly angular and flake-like due to the grinding process. Invarious embodiments of the present invention, such non-spherical powderparticles are mixed with substantially spherical plasma-densifiedparticles of other constituent metals, thereby maximizing particlepacking efficiency and minimizing the amount of trapped volatile specieswithin the final wire.

In accordance with various embodiments of the invention, the HEA or MPEAfeedstock wire is formed by, e.g., drawing and/or other mechanicaldeformation (e.g., swaging, pilgering, extrusion, etc.) of a preformthat has the shape of, for example, a rod or a bar. The resulting wiremay be utilized in an additive manufacturing process to form athree-dimensional part composed of the alloy of the wire. In exemplaryembodiments, the wire is fed toward a movable platform, and the tip ofthe wire is melted by, e.g., an electron beam or a laser. The platformmoves such that the molten wire traces out the pattern of asubstantially two-dimensional slice of the final part; in this manner,the final part is fabricated in layer-by-layer fashion via melting andrapid solidification of the wire.

Wire in accordance with embodiments of the invention may also beutilized in a variety of different wire-fed welding applications (e.g.,MIG welding, welding repair) in which an electric arc is struck betweenthe wire and a workpiece, causing part of the wire to fuse with theworkpiece.

Various embodiments of the invention fabricate and utilize HEAsincluding, consisting essentially of, or consisting of five or moreelements such as five or more of Nb, Ta, Mo, W, Ti, Hf, V, Zr, Al,and/or Cr. Exemplary HEAs in accordance with embodiments of theinvention include MoTaTiZrHf, MoTaNbTiZrHf, MoTaNbWTiV, NbTiHfZrCr,NbTiHfZrV, and NbTaMoWX, where X is one or more of V, Cr, Ti, Zr, Hf,and Al. Various embodiments of the invention fabricate and utilizemulti-principal element alloys (MPEAs) that include, consist essentiallyof, or consist of four or more elements such as four or more of Nb, Ta,Mo, W, Ti, Hf, V, Zr, Al, and/or Cr. Unless otherwise indicated,references herein to HEAs and/or the fabrication and use of HEAscontaining five or more elements also encompass and are applicable toMPEAs having four or more elements and their fabrication and use. Foreach alloy in accordance with embodiments of the invention, the variouselemental constituents may be present within the alloy in equiatomic orsubstantially equiatomic proportions. In other embodiments, one or more,or even each, of the elemental constituents is present within the alloyat an atomic concentration between 5% and 35%. In various embodiments,two or more of the elemental constituents are present in the alloy atapproximately equal concentrations, and those concentrations aredifferent from that of one or more other elemental constituents in thealloy. For example, two of the elemental constituents may be present inthe alloy at approximately 40% (atomic), while the other 20% of thealloy is composed of the two or more other constituents, which may ormay not be present in concentrations that are approximately equal toeach other.

As utilized herein, the term “substantially spherical” means sphericalto within ±10%, and in some embodiments, ±5% in any direction—i.e., theeccentricity in any direction does not exceed 5% or 10%. As utilizedherein, “non-spherical” means elongated with an aspect ratio of at least2:1, acicular, having at least one flat surface (e.g., a flake with twoopposed flat surfaces), having at least one corner or vertex, orpolyhedral.

In an aspect, embodiments of the invention feature a method offabricating a metallic wire. One or more first metal powders and one ormore second metal powders are combined to form at least a portion of apreform. Each of the first metal powders includes, consists essentiallyof, or consists of substantially spherical particles. Each of the secondmetal powders includes, consists essentially of, or consists ofnon-spherical particles. The one or more first metal powders are mixedwith the one or more second metal particles such that a composition ofthe preform is substantially homogenous along at least a portion of thelength of the preform. The diameter (or other lateral dimension such asa width) of the preform is reduced via one or more mechanicaldeformation processes to form a metallic wire. The metallic wireincludes, consists essentially of, or consists of a high-entropy alloythat includes, consists essentially of, or consists of five or moremetallic elements. Each first metal powder includes, consistsessentially of, or consists of at least one of the metallic elements.Each second metal powder includes, consists essentially of, or consistsof at least one of the metallic elements.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The five or more metallic elements mayinclude, consist essentially of, or consist of at least five of Nb, Ta,Mo, W, Ti, Hf, V, Zr, Al, or Cr. At least one first metal powder may bean elemental powder including, consisting essentially of, or consistingof one of the metallic elements. At least one first metal powder may bean alloy powder including, consisting essentially of, or consisting oftwo or more of the metallic elements. At least one second metal powdermay be an elemental powder including, consisting essentially of, orconsisting of one of the metallic elements. At least one second metalpowder may be an alloy powder including, consisting essentially of, orconsisting of two or more of the metallic elements. At least some of thenon-spherical particles of at least one second metal powder may beangular flakes. The concentration of oxygen, carbon, calcium, sodium,antimony, phosphorus, sulfur, and/or nitrogen of at least one of thefirst metal powders and/or at least one of the second metal powders,and/or of the wire itself, may be 300 ppm or less, 200 ppm or less, 100ppm or less, 50 ppm or less, 25 ppm or less, or 10 ppm or less. The oneor more mechanical deformation processes may include, consistessentially of, or consist of drawing, pilgering, swaging, extrusion,and/or rolling.

The preform may include one or more metallic tubes surrounding the oneor more first metal powders and the one or more second metal powders.Each metallic tube may include, consist essentially of, or consist of atleast one of the metallic elements. The one or more first metal powdersand the one or more second metal powders may be combined within one ormore sacrificial tubes. One or more (or even all) of the sacrificialtubes may be removed before, during, and/or after the diameter (or otherlateral dimension) of the preform is reduced. Removing one or more ofthe sacrificial tubes may include, consist essentially of, or consist ofmelting and/or etching (e.g., wet chemical (e.g., acid) etching and/ordry (e.g., plasma) etching).

At least one of the first metal powders may be provided by a processincluding, consisting essentially of, or consisting of (a) providing aplurality of metal particulates and/or metal wire, (b) feeding the metalparticulates and/or wire into a plasma, thereby at least partiallymelting (and/or atomizing and/or breaking apart) the metal particulatesand/or wire, and (c) cooling the at least partially melted metalparticulates and/or wire portions to form substantially sphericalparticles. At least one of the second metal powders may be provided by aprocess including, consisting essentially of, or consisting of (a)hydrogenating metal to form a metal hydride, (b) mechanically grindingthe metal hydride into a plurality of non-spherical particles, and (c)dehydrogenating the non-spherical metal hydride particles. An averageparticle size of at least one of the first metal powders may range fromapproximately 15 μm to approximately 45 μm. An average particle size ofat least one of the second metal powders may be greater thanapproximately 50 μm. An average particle size of at least one of thesecond metal powders may range from approximately 50 μm to approximately100 μm or approximately 200 μm. An average particle size of one or more(or even all) of the first metal powders may be smaller than an averageparticle size of one or more (or even all) of the second metal powders.Embodiments of the invention may include wires formed by one or more ofthe above methods.

The wire may be utilized in an additive manufacturing process to form athree-dimensional part in, e.g., layer-by-layer fashion. A tip of thewire may be translated relative to a platform (i.e., the wire may betranslated, the platform may be translated, or both may be translated).During the relative translation, the tip of the wire may be melted usingan energy source to form a molten bead including, consisting essentiallyof, or consisting of the five or more metallic elements. The bead maycool to form at least a portion of a layer of a three-dimensional part.These steps may be repeated one or more times to produce at least aportion of the three-dimensional part. The three-dimensional part mayinclude, consist essentially of, or consist of the high-entropy alloy.Embodiments of the invention may include three-dimensional parts formedaccording to any of the above methods.

In another aspect, embodiments of the invention feature a method offabricating a metallic wire or wire preform that includes, consistsessentially of, or consists of a high-entropy alloy including,consisting essentially of, or consisting of five or more metallicelements. A metallic tube is provided. The metallic tube includes,consists essentially of, or consists of at least one of the metallicelements of the high-entropy alloy. One or more first metal powders andone or more second metal powders are combined within the metallic tube.Each of the first metal powders includes, consists essentially of, orconsists of substantially spherical particles. Each of the second metalpowders includes, consists essentially of, or consists of non-sphericalparticles. The one or more first metal powders are mixed with the one ormore second metal particles such that a composition of the combinedpowders is substantially homogenous along at least a portion of thelength of the metallic tube, thereby forming the metallic wire or wirepreform. Each first metal powder includes, consists essentially of, orconsists of at least one of the metallic elements of the high-entropyalloy. Each second metal powder includes, consists essentially of, orconsists of at least one of the metallic elements of the high-entropyalloy.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The diameter (or other lateraldimension, e.g., width) of the metallic wire or wire preform may bereduced via one or more mechanical deformation processes. The one ormore mechanical deformation processes may include, consist essentiallyof, or consist of drawing, pilgering, swaging, extrusion, and/orrolling. The five or more metallic elements may include, consistessentially of, or consist of at least five of Nb, Ta, Mo, W, Ti, Hf, V,Zr, Al, and/or Cr. At least one first metal powder may be an elementalpowder including, consisting essentially of, or consisting of one of themetallic elements. At least one first metal powder may be an alloypowder including, consisting essentially of, or consisting of two ormore of the metallic elements. At least one second metal powder may bean elemental powder including, consisting essentially of, or consistingof one of the metallic elements. At least one second metal powder may bean alloy powder including, consisting essentially of, or consisting oftwo or more of the metallic elements. At least some of the non-sphericalparticles of at least one second metal powder may be angular flakes. Theconcentration of oxygen, carbon, calcium, sodium, antimony, phosphorus,sulfur, and/or nitrogen of at least one of the first metal powders,and/or at least one of the second metal powders, and/or of the metallictube, and/or of the wire or wire preform itself, may be 300 ppm or less,200 ppm or less, 100 ppm or less, 50 ppm or less, 25 ppm or less, or 10ppm or less. The metallic tube may include, consist essentially of, orconsist of one of the metallic elements. The metallic tube may be analloy tube including, consisting essentially of, or consisting of two ormore of the metallic elements.

At least one of the first metal powders may be provided by a processincluding, consisting essentially of, or consisting of (a) providing aplurality of metal particulates and/or metal wire, (b) feeding the metalparticulates and/or wire into a plasma, thereby at least partiallymelting (and/or atomizing and/or breaking apart) the metal particulatesand/or wire, and (c) cooling the at least partially melted metalparticulates and/or wire portions to form substantially sphericalparticles. At least one of the second metal powders may be provided by aprocess including, consisting essentially of, or consisting of (a)hydrogenating metal to form a metal hydride, (b) mechanically grindingthe metal hydride into a plurality of non-spherical particles, and (c)dehydrogenating the non-spherical metal hydride particles. An averageparticle size of at least one of the first metal powders may range fromapproximately 15 μm to approximately 45 μm. An average particle size ofat least one of the second metal powders may be greater thanapproximately 50 μm. An average particle size of at least one of thesecond metal powders may range from approximately 50 μm to approximately100 μm or approximately 200 μm. An average particle size of one or more(or even all) of the first metal powders may be smaller than an averageparticle size of one or more (or even all) of the second metal powders.Embodiments of the invention may include wires or wire preforms formedby one or more of the above methods.

The wire may be utilized in an additive manufacturing process to form athree-dimensional part in, e.g., layer-by-layer fashion. A tip of thewire may be translated relative to a platform (i.e., the wire may betranslated, the platform may be translated, or both may be translated).During the relative translation, the tip of the wire may be melted usingan energy source to form a molten bead including, consisting essentiallyof, or consisting of the five or more metallic elements. The bead maycool to form at least a portion of a layer of a three-dimensional part.These steps may be repeated one or more times to produce at least aportion of the three-dimensional part. The three-dimensional part mayinclude, consist essentially of, or consist of the high-entropy alloy.Embodiments of the invention may include three-dimensional parts formedaccording to any of the above methods.

In yet another aspect, embodiments of the invention feature a method offorming a three-dimensional part including, consisting essentially of,or consisting of a high entropy alloy by additive manufacturing. Thehigh entropy alloy includes, consists essentially of, or consists offive or more metallic elements selected from the group consisting of Nb,Ta, Mo, W, Ti, Hf, V, Zr, Al, and Cr. In a step (a), a wire is provided.The wire includes, consists essentially of, or consists of asubstantially homogenous assemblage of one or more first metal powdersand one or more second metal powders. Each first metal powder includes,consists essentially of, or consists of one or more of the metallicelements. Each second metal powder includes, consists essentially of, orconsists of one or more of the metallic elements. Particles of eachfirst metal powder are substantially spherical. Particles of each secondmetal powder are non-spherical. In a step (b), a tip of the wire istranslated relative to a platform (i.e., the wire may be translated, theplatform may be translated, or both may be translated). In a step (c),during the relative translation, the tip of the wire is melted using anenergy source to form a molten bead including, consisting essentiallyof, or consisting of the five or more metallic elements. The bead coolsto form at least a portion of a layer of a three-dimensional part. Steps(b) and (c) may be repeated one or more times to produce at least aportion of the three-dimensional part. The three-dimensional partincludes, consists essentially of, or consists of the high-entropyalloy.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. At least one first metal powder may bean elemental powder including, consisting essentially of, or consistingof one of the metallic elements. At least one first metal powder may bean alloy powder including, consisting essentially of, or consisting oftwo or more of the metallic elements. At least one second metal powdermay be an elemental powder including, consisting essentially of, orconsisting of one of the metallic elements. At least one second metalpowder may be an alloy powder including, consisting essentially of, orconsisting of two or more of the metallic elements. At least some of thenon-spherical particles of at least one second metal powder may beangular flakes. The wire may include one or more metallic tubessurrounding the one or more first metal powders and the one or moresecond metal powders. Each metallic tube may include, consistessentially of, or consist of at least one of the metallic elements. Theconcentration of oxygen, carbon, calcium, sodium, antimony, phosphorus,sulfur, and/or nitrogen of at least one of the first metal powders,and/or at least one of the second metal powders, and/or at least onemetallic tube, and/or of the wire itself, may be 300 ppm or less, 200ppm or less, 100 ppm or less, 50 ppm or less, 25 ppm or less, or 10 ppmor less. Embodiments of the invention may include three-dimensionalparts formed according to any of the above methods.

In another aspect, embodiments of the invention feature ahigh-entropy-alloy wire or wire preform including, consistingessentially of, or consisting of five or more metallic elements. Thewire or wire preform includes, consists essentially of, or consists ofan assemblage of one or more first metal powders and one or more secondmetal powders. Each first metal powder includes, consists essentiallyof, or consists of one or more of the metallic elements. Each secondmetal powder includes, consists essentially of, or consists of one ormore of the metallic elements. Particles of each first metal powder aresubstantially spherical. Particles of each second metal powder arenon-spherical.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The five or more metallic elements mayinclude, consist essentially of, or consist of at least five of Nb, Ta,Mo, W, Ti, Hf, V, Zr, Al, and/or Cr. At least one first metal powder maybe an elemental powder including, consisting essentially of, orconsisting of one of the metallic elements. At least one first metalpowder may be an alloy powder including, consisting essentially of, orconsisting of two or more of the metallic elements. At least one secondmetal powder may be an elemental powder including, consistingessentially of, or consisting of one of the metallic elements. At leastone second metal powder may be an alloy powder including, consistingessentially of, or consisting of two or more of the metallic elements.At least some of the non-spherical particles of at least one secondmetal powder may be angular flakes. The wire or wire preform may includeone or more metallic tubes surrounding the one or more first metalpowders and the one or more second metal powders. Each metallic tube mayinclude, consist essentially of, or consist of at least one of themetallic elements. The concentration of oxygen, carbon, calcium, sodium,antimony, phosphorus, sulfur, and/or nitrogen of at least one of thefirst metal powders, and/or at least one of the second metal powders,and/or of the metallic tube, and/or of the wire or wire preform itself,may be 300 ppm or less, 200 ppm or less, 100 ppm or less, 50 ppm orless, 25 ppm or less, or 10 ppm or less.

In an aspect, embodiments of the invention feature a method offabricating a metallic wire. One or more first metal powders and one ormore second metal powders are combined to form at least a portion of apreform. Each of the first metal powders includes, consists essentiallyof, or consists of substantially spherical particles. Each of the secondmetal powders includes, consists essentially of, or consists ofnon-spherical particles. The one or more first metal powders are mixedwith the one or more second metal particles such that a composition ofthe preform is substantially homogenous along at least a portion of thelength of the preform. The diameter (or other lateral dimension such asa width) of the preform is reduced via one or more mechanicaldeformation processes to form a metallic wire. The metallic wireincludes, consists essentially of, or consists of (1) a high-entropyalloy that includes, consists essentially of, or consists of five ormore metallic elements or (2) a multi-principal element alloy thatincludes, consists essentially of, or consists of four or more metallicelements. Each first metal powder includes, consists essentially of, orconsists of at least one of the metallic elements. Each second metalpowder includes, consists essentially of, or consists of at least one ofthe metallic elements.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The metallic elements may include,consist essentially of, or consist of at least four or at least five ofNb, Ta, Mo, W, Ti, Hf, V, Zr, Al, or Cr. At least one first metal powdermay be an elemental powder including, consisting essentially of, orconsisting of one of the metallic elements. At least one first metalpowder may be an alloy powder including, consisting essentially of, orconsisting of two or more of the metallic elements. At least one secondmetal powder may be an elemental powder including, consistingessentially of, or consisting of one of the metallic elements. At leastone second metal powder may be an alloy powder including, consistingessentially of, or consisting of two or more of the metallic elements.At least some of the non-spherical particles of at least one secondmetal powder may be angular flakes. The concentration of oxygen, carbon,calcium, sodium, antimony, phosphorus, sulfur, and/or nitrogen of atleast one of the first metal powders and/or at least one of the secondmetal powders, and/or of the wire itself, may be 300 ppm or less, 200ppm or less, 100 ppm or less, 50 ppm or less, 25 ppm or less, or 10 ppmor less. The one or more mechanical deformation processes may include,consist essentially of, or consist of drawing, pilgering, swaging,extrusion, and/or rolling.

The preform may include one or more metallic tubes surrounding the oneor more first metal powders and the one or more second metal powders.Each metallic tube may include, consist essentially of, or consist of atleast one of the metallic elements. The one or more first metal powdersand the one or more second metal powders may be combined within one ormore sacrificial tubes. One or more (or even all) of the sacrificialtubes may be removed before, during, and/or after the diameter (or otherlateral dimension) of the preform is reduced. Removing one or more ofthe sacrificial tubes may include, consist essentially of, or consist ofmelting and/or etching (e.g., wet chemical (e.g., acid) etching and/ordry (e.g., plasma) etching).

At least one of the first metal powders may be provided by a processincluding, consisting essentially of, or consisting of (a) providing aplurality of metal particulates and/or metal wire, (b) feeding the metalparticulates and/or wire into a plasma, thereby at least partiallymelting (and/or atomizing and/or breaking apart) the metal particulatesand/or wire, and (c) cooling the at least partially melted metalparticulates and/or wire portions to form substantially sphericalparticles. At least one of the second metal powders may be provided by aprocess including, consisting essentially of, or consisting of (a)hydrogenating metal to form a metal hydride, (b) mechanically grindingthe metal hydride into a plurality of non-spherical particles, and (c)dehydrogenating the non-spherical metal hydride particles. An averageparticle size of at least one of the first metal powders may range fromapproximately 15 μm to approximately 45 μm. An average particle size ofat least one of the second metal powders may be greater thanapproximately 50 μm. An average particle size of at least one of thesecond metal powders may range from approximately 50 μm to approximately100 μm or approximately 200 μm. An average particle size of one or more(or even all) of the first metal powders may be smaller than an averageparticle size of one or more (or even all) of the second metal powders.Embodiments of the invention may include wires formed by one or more ofthe above methods.

The wire may be utilized in an additive manufacturing process to form athree-dimensional part in, e.g., layer-by-layer fashion. A tip of thewire may be translated relative to a platform (i.e., the wire may betranslated, the platform may be translated, or both may be translated).During the relative translation, the tip of the wire may be melted usingan energy source to form a molten bead including, consisting essentiallyof, or consisting of the four or more metallic elements or the five ormore metallic elements. The bead may cool to form at least a portion ofa layer of a three-dimensional part. These steps may be repeated one ormore times to produce at least a portion of the three-dimensional part.The three-dimensional part may include, consist essentially of, orconsist of the high-entropy alloy or the multi-principal element alloy.Embodiments of the invention may include three-dimensional parts formedaccording to any of the above methods.

In another aspect, embodiments of the invention feature a method offabricating a metallic wire or wire preform that includes, consistsessentially of, or consists of (1) a high-entropy alloy including,consisting essentially of, or consisting of five or more metallicelements or (2) a multi-principal element alloy including, consistingessentially of, or consisting of four or more metallic elements. Ametallic tube is provided. The metallic tube includes, consistsessentially of, or consists of at least one of the metallic elements ofthe high-entropy alloy or the multi-principal element alloy. One or morefirst metal powders and one or more second metal powders are combinedwithin the metallic tube. Each of the first metal powders includes,consists essentially of, or consists of substantially sphericalparticles. Each of the second metal powders includes, consistsessentially of, or consists of non-spherical particles. The one or morefirst metal powders are mixed with the one or more second metalparticles such that a composition of the combined powders issubstantially homogenous along at least a portion of the length of themetallic tube, thereby forming the metallic wire or wire preform. Eachfirst metal powder includes, consists essentially of, or consists of atleast one of the metallic elements of the high-entropy alloy or themulti-principal element alloy. Each second metal powder includes,consists essentially of, or consists of at least one of the metallicelements of the high-entropy alloy or the multi-principal element alloy.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The diameter (or other lateraldimension, e.g., width) of the metallic wire or wire preform may bereduced via one or more mechanical deformation processes. The one ormore mechanical deformation processes may include, consist essentiallyof, or consist of drawing, pilgering, swaging, extrusion, and/orrolling. The metallic elements may include, consist essentially of, orconsist of at least four of or at least five of Nb, Ta, Mo, W, Ti, Hf,V, Zr, Al, and/or Cr. At least one first metal powder may be anelemental powder including, consisting essentially of, or consisting ofone of the metallic elements. At least one first metal powder may be analloy powder including, consisting essentially of, or consisting of twoor more of the metallic elements. At least one second metal powder maybe an elemental powder including, consisting essentially of, orconsisting of one of the metallic elements. At least one second metalpowder may be an alloy powder including, consisting essentially of, orconsisting of two or more of the metallic elements. At least some of thenon-spherical particles of at least one second metal powder may beangular flakes. The concentration of oxygen, carbon, calcium, sodium,antimony, phosphorus, sulfur, and/or nitrogen of at least one of thefirst metal powders, and/or at least one of the second metal powders,and/or of the metallic tube, and/or of the wire itself, may be 300 ppmor less, 200 ppm or less, 100 ppm or less, 50 ppm or less, 25 ppm orless, or 10 ppm or less. The metallic tube may include, consistessentially of, or consist of one of the metallic elements. The metallictube may be an alloy tube including, consisting essentially of, orconsisting of two or more of the metallic elements.

At least one of the first metal powders may be provided by a processincluding, consisting essentially of, or consisting of (a) providing aplurality of metal particulates and/or metal wire, (b) feeding the metalparticulates and/or wire into a plasma, thereby at least partiallymelting (and/or atomizing and/or breaking apart) the metal particulatesand/or wire, and (c) cooling the at least partially melted metalparticulates and/or wire portions to form substantially sphericalparticles. At least one of the second metal powders may be provided by aprocess including, consisting essentially of, or consisting of (a)hydrogenating metal to form a metal hydride, (b) mechanically grindingthe metal hydride into a plurality of non-spherical particles, and (c)dehydrogenating the non-spherical metal hydride particles. An averageparticle size of at least one of the first metal powders may range fromapproximately 15 μm to approximately 45 μm. An average particle size ofat least one of the second metal powders may be greater thanapproximately 50 μm. An average particle size of at least one of thesecond metal powders may range from approximately 50 μm to approximately100 μm or approximately 200 μm. An average particle size of one or more(or even all) of the first metal powders may be smaller than an averageparticle size of one or more (or even all) of the second metal powders.Embodiments of the invention may include wires or wire preforms formedby one or more of the above methods.

The wire may be utilized in an additive manufacturing process to form athree-dimensional part in, e.g., layer-by-layer fashion. A tip of thewire may be translated relative to a platform (i.e., the wire may betranslated, the platform may be translated, or both may be translated).During the relative translation, the tip of the wire may be melted usingan energy source to form a molten bead including, consisting essentiallyof, or consisting of the four or more metallic elements or the five ormore metallic elements. The bead may cool to form at least a portion ofa layer of a three-dimensional part. These steps may be repeated one ormore times to produce at least a portion of the three-dimensional part.The three-dimensional part may include, consist essentially of, orconsist of the high-entropy alloy or the multi-principal element alloy.Embodiments of the invention may include three-dimensional parts formedaccording to any of the above methods.

In yet another aspect, embodiments of the invention feature a method offorming a three-dimensional part including, consisting essentially of,or consisting of a high-entropy alloy or a multi-principal element alloyby additive manufacturing. The high-entropy alloy includes, consistsessentially of, or consists of five or more metallic elements selectedfrom the group consisting of Nb, Ta, Mo, W, Ti, Hf, V, Zr, Al, and Cr.The multi-principal element alloy includes, consists essentially of, orconsists of four or more metallic elements selected from the groupconsisting of Nb, Ta, Mo, W, Ti, Hf, V, Zr, Al, and Cr. In a step (a), awire is provided. The wire includes, consists essentially of, orconsists of a substantially homogenous assemblage of one or more firstmetal powders and one or more second metal powders. Each first metalpowder includes, consists essentially of, or consists of one or more ofthe metallic elements. Each second metal powder includes, consistsessentially of, or consists of one or more of the metallic elements.Particles of each first metal powder are substantially spherical.Particles of each second metal powder are non-spherical. In a step (b),a tip of the wire is translated relative to a platform (i.e., the wiremay be translated, the platform may be translated, or both may betranslated). In a step (c), during the relative translation, the tip ofthe wire is melted using an energy source to form a molten beadincluding, consisting essentially of, or consisting of the four or moremetallic elements or the five or more metallic elements. The bead coolsto form at least a portion of a layer of a three-dimensional part. Steps(b) and (c) may be repeated one or more times to produce at least aportion of the three-dimensional part. The three-dimensional partincludes, consists essentially of, or consists of the high-entropy alloyor the multi-principal element alloy.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. At least one first metal powder may bean elemental powder including, consisting essentially of, or consistingof one of the metallic elements. At least one first metal powder may bean alloy powder including, consisting essentially of, or consisting oftwo or more of the metallic elements. At least one second metal powdermay be an elemental powder including, consisting essentially of, orconsisting of one of the metallic elements. At least one second metalpowder may be an alloy powder including, consisting essentially of, orconsisting of two or more of the metallic elements. At least some of thenon-spherical particles of at least one second metal powder may beangular flakes. The wire may include one or more metallic tubessurrounding the one or more first metal powders and the one or moresecond metal powders. Each metallic tube may include, consistessentially of, or consist of at least one of the metallic elements. Theconcentration of oxygen, carbon, calcium, sodium, antimony, phosphorus,sulfur, and/or nitrogen of at least one of the first metal powders,and/or at least one of the second metal powders, and/or at least onemetallic tube, and/or of the wire itself, may be 300 ppm or less, 200ppm or less, 100 ppm or less, 50 ppm or less, 25 ppm or less, or 10 ppmor less. Embodiments of the invention may include three-dimensionalparts formed according to any of the above methods.

In another aspect, embodiments of the invention feature amulti-principal element alloy wire or wire preform including, consistingessentially of, or consisting of four or more metallic elements. Thewire or wire preform includes, consists essentially of, or consists ofan assemblage of one or more first metal powders and one or more secondmetal powders. Each first metal powder includes, consists essentiallyof, or consists of one or more of the metallic elements. Each secondmetal powder includes, consists essentially of, or consists of one ormore of the metallic elements. Particles of each first metal powder aresubstantially spherical. Particles of each second metal powder arenon-spherical.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The four or more metallic elements mayinclude, consist essentially of, or consist of at least four of Nb, Ta,Mo, W, Ti, Hf, V, Zr, Al, and/or Cr. At least one first metal powder maybe an elemental powder including, consisting essentially of, orconsisting of one of the metallic elements. At least one first metalpowder may be an alloy powder including, consisting essentially of, orconsisting of two or more of the metallic elements. At least one secondmetal powder may be an elemental powder including, consistingessentially of, or consisting of one of the metallic elements. At leastone second metal powder may be an alloy powder including, consistingessentially of, or consisting of two or more of the metallic elements.At least some of the non-spherical particles of at least one secondmetal powder may be angular flakes. The wire may include one or moremetallic tubes surrounding the one or more first metal powders and theone or more second metal powders. Each metallic tube may include,consist essentially of, or consist of at least one of the metallicelements. The concentration of oxygen, carbon, calcium, sodium,antimony, phosphorus, sulfur, and/or nitrogen of at least one of thefirst metal powders, and/or at least one of the second metal powders,and/or of the metallic tube, and/or of the wire or wire preform itself,may be 300 ppm or less, 200 ppm or less, 100 ppm or less, 50 ppm orless, 25 ppm or less, or 10 ppm or less.

In yet another aspect, embodiments of the invention feature a method offorming a three-dimensional part including, consisting essentially of,or consisting of a high-entropy alloy or a multi-principal element alloyby additive manufacturing. The high-entropy alloy includes, consistsessentially of, or consists of five or more metallic elements selectedfrom the group consisting of Nb, Ta, Mo, W, Ti, Hf, V, Zr, Al, and Cr.The multi-principal element alloy includes, consists essentially of, orconsists of four or more metallic elements selected from the groupconsisting of Nb, Ta, Mo, W, Ti, Hf, V, Zr, Al, and Cr. In a step (a), awire preform is provided. The wire preform includes, consistsessentially of, or consists of a substantially homogenous assemblage ofone or more first metal powders and one or more second metal powders.Each first metal powder includes, consists essentially of, or consistsof one or more of the metallic elements. Each second metal powderincludes, consists essentially of, or consists of one or more of themetallic elements. Particles of each first metal powder aresubstantially spherical. Particles of each second metal powder arenon-spherical. In a step (b), a diameter (or other lateral dimensionsuch as width) of the wire preform is reduced via one or more mechanicaldeformation processes, thereby forming a metallic wire. In a step (c), atip of the wire is translated relative to a platform (i.e., the wire maybe translated, the platform may be translated, or both may betranslated). In a step (d), during the relative translation, the tip ofthe wire is melted using an energy source to form a molten beadincluding, consisting essentially of, or consisting of the four or moremetallic elements or the five or more metallic elements. The bead coolsto form at least a portion of a layer of a three-dimensional part. Steps(c) and (d) may be repeated one or more times to produce at least aportion of the three-dimensional part. The three-dimensional partincludes, consists essentially of, or consists of the high-entropy alloyor the multi-principal element alloy.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The one or more mechanical deformationprocesses may include, consist essentially of, or consist of drawing,pilgering, swaging, extrusion, and/or rolling. At least one first metalpowder may be an elemental powder including, consisting essentially of,or consisting of one of the metallic elements. At least one first metalpowder may be an alloy powder including, consisting essentially of, orconsisting of two or more of the metallic elements. At least one secondmetal powder may be an elemental powder including, consistingessentially of, or consisting of one of the metallic elements. At leastone second metal powder may be an alloy powder including, consistingessentially of, or consisting of two or more of the metallic elements.At least some of the non-spherical particles of at least one secondmetal powder may be angular flakes. The wire preform may include one ormore metallic tubes surrounding the one or more first metal powders andthe one or more second metal powders. Each metallic tube may include,consist essentially of, or consist of at least one of the metallicelements. The concentration of oxygen, carbon, calcium, sodium,antimony, phosphorus, sulfur, and/or nitrogen of at least one of thefirst metal powders, and/or at least one of the second metal powders,and/or at least one metallic tube, and/or of the wire preform, and/or ofthe wire itself, may be 300 ppm or less, 200 ppm or less, 100 ppm orless, 50 ppm or less, 25 ppm or less, or 10 ppm or less. Embodiments ofthe invention may include three-dimensional parts formed according toany of the above methods.

In an aspect, embodiments of the invention feature a high-entropy-alloywire including, consisting essentially of, or consisting of five or moremetallic elements. The wire includes, consists essentially of, orconsists of an assemblage of one or more first metal powders and one ormore second metal powders. Each first metal powder includes, consistsessentially of, or consists of one or more of the metallic elements.Each second metal powder includes, consists essentially of, or consistsof one or more of the metallic elements. At least some particles of atleast one first metal powder are substantially spherical. At least someparticles of at least one second metal powder are elongated in the axialdirection and extend at least partially around particles of the one ormore first metal powders.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. At least some of the particles of eachof the first metal powders may be substantially spherical. At least someparticles of at least one first metal powder may be elongated in theaxial direction. At least some particles of each of the first metalpowders may be elongated in the axial direction. Particles of at leastone first metal powder may be less ductile than particles of at leastone second metal powder. Particles of all of the first metal powders maybe less ductile than particles of all of the second metal powders. Theone or more first metal powders may include, consist essentially of, orconsist of Mo and/or W. The one or more second metal powders mayinclude, consist essentially of, or consist of Ta and/or Nb.

The five or more metallic elements may include, consist essentially of,or consist of at least five of Nb, Ta, Mo, W, Ti, Hf, V, Zr, Al, and/orCr. At least one first metal powder may be an elemental powderincluding, consisting essentially of, or consisting of one of themetallic elements. At least one first metal powder may be an alloypowder including, consisting essentially of, or consisting of two ormore of the metallic elements. At least one second metal powder may bean elemental powder including, consisting essentially of, or consistingof one of the metallic elements. At least one second metal powder may bean alloy powder including, consisting essentially of, or consisting oftwo or more of the metallic elements. The wire may include one or moremetallic tubes surrounding the one or more first metal powders and theone or more second metal powders. Each metallic tube may include,consist essentially of, or consist of at least one of the metallicelements. The concentration of oxygen, carbon, calcium, sodium,antimony, phosphorus, sulfur, and/or nitrogen of at least one of thefirst metal powders, and/or at least one of the second metal powders,and/or of the metallic tube, and/or of the wire itself, may be 300 ppmor less, 200 ppm or less, 100 ppm or less, 50 ppm or less, 25 ppm orless, or 10 ppm or less.

In another aspect, embodiments of the invention feature amulti-principal element alloy wire or wire preform including, consistingessentially of, or consisting of four or more metallic elements. Thewire includes, consists essentially of, or consists of an assemblage ofone or more first metal powders and one or more second metal powders.Each first metal powder includes, consists essentially of, or consistsof one or more of the metallic elements. Each second metal powderincludes, consists essentially of, or consists of one or more of themetallic elements. At least some particles of at least one first metalpowder are substantially spherical. At least some particles of at leastone second metal powder are elongated in the axial direction and extendat least partially around particles of the one or more first metalpowders.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. At least some of the particles of eachof the first metal powders may be substantially spherical. At least someparticles of at least one first metal powder may be elongated in theaxial direction. At least some particles of each of the first metalpowders may be elongated in the axial direction. Particles of at leastone first metal powder may be less ductile than particles of at leastone second metal powder. Particles of all of the first metal powders maybe less ductile than particles of all of the second metal powders. Theone or more first metal powders may include, consist essentially of, orconsist of Mo and/or W. The one or more second metal powders mayinclude, consist essentially of, or consist of Ta and/or Nb.

The four or more metallic elements may include, consist essentially of,or consist of at least four of Nb, Ta, Mo, W, Ti, Hf, V, Zr, Al, and/orCr. At least one first metal powder may be an elemental powderincluding, consisting essentially of, or consisting of one of themetallic elements. At least one first metal powder may be an alloypowder including, consisting essentially of, or consisting of two ormore of the metallic elements. At least one second metal powder may bean elemental powder including, consisting essentially of, or consistingof one of the metallic elements. At least one second metal powder may bean alloy powder including, consisting essentially of, or consisting oftwo or more of the metallic elements. The wire may include one or moremetallic tubes surrounding the one or more first metal powders and theone or more second metal powders. Each metallic tube may include,consist essentially of, or consist of at least one of the metallicelements. The concentration of oxygen, carbon, calcium, sodium,antimony, phosphorus, sulfur, and/or nitrogen of at least one of thefirst metal powders, and/or at least one of the second metal powders,and/or of the metallic tube, and/or of the wire itself, may be 300 ppmor less, 200 ppm or less, 100 ppm or less, 50 ppm or less, 25 ppm orless, or 10 ppm or less.

In yet another aspect, embodiments of the invention feature a method offorming a three-dimensional part including, consisting essentially of,or consisting of a high-entropy alloy or a multi-principal element alloyby additive manufacturing. The high-entropy alloy includes, consistsessentially of, or consists of five or more metallic elements selectedfrom the group consisting of Nb, Ta, Mo, W, Ti, Hf, V, Zr, Al, and Cr.The multi-principal element alloy includes, consists essentially of, orconsists of four or more metallic elements selected from the groupconsisting of Nb, Ta, Mo, W, Ti, Hf, V, Zr, Al, and Cr. In a step (a), awire that extends in an axial direction is provided. The wire includes,consists essentially of, or consists of a substantially homogenousassemblage of one or more first metal powders and one or more secondmetal powders. Each first metal powder includes, consists essentiallyof, or consists of one or more of the metallic elements. Each secondmetal powder includes, consists essentially of, or consists of one ormore of the metallic elements. At least some particles of at least onefirst metal powder are substantially spherical. At least some particlesof at least one second metal powder are elongated in the axial directionand extend at least partially around particles of at least one of thefirst metal powders. In a step (b), a tip of the wire is translatedrelative to a platform (i.e., the wire may be translated, the platformmay be translated, or both may be translated). In a step (c), during therelative translation, the tip of the wire is melted using an energysource to form a molten bead including, consisting essentially of, orconsisting of the four or more metallic elements or the five or moremetallic elements. The bead cools to form at least a portion of a layerof a three-dimensional part. Steps (b) and (c) may be repeated one ormore times to produce at least a portion of the three-dimensional part.The three-dimensional part includes, consists essentially of, orconsists of the high-entropy alloy or the multi-principal element alloy.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. At least some of the particles of eachof the first metal powders may be substantially spherical. At least someparticles of at least one first metal powder may be elongated in theaxial direction. At least some particles of each of the first metalpowders may be elongated in the axial direction. Particles of at leastone first metal powder may be less ductile than particles of at leastone second metal powder. Particles of all of the first metal powders maybe less ductile than particles of all of the second metal powders. Theone or more first metal powders may include, consist essentially of, orconsist of Mo and/or W. The one or more second metal powders mayinclude, consist essentially of, or consist of Ta and/or Nb.

At least one first metal powder may be an elemental powder including,consisting essentially of, or consisting of one of the metallicelements. At least one first metal powder may be an alloy powderincluding, consisting essentially of, or consisting of two or more ofthe metallic elements. At least one second metal powder may be anelemental powder including, consisting essentially of, or consisting ofone of the metallic elements. At least one second metal powder may be analloy powder including, consisting essentially of, or consisting of twoor more of the metallic elements. The wire may include one or moremetallic tubes surrounding the one or more first metal powders and theone or more second metal powders. Each metallic tube may include,consist essentially of, or consist of at least one of the metallicelements. The concentration of oxygen, carbon, calcium, sodium,antimony, phosphorus, sulfur, and/or nitrogen of at least one of thefirst metal powders, and/or at least one of the second metal powders,and/or at least one metallic tube, and/or of the wire itself, may be 300ppm or less, 200 ppm or less, 100 ppm or less, 50 ppm or less, 25 ppm orless, or 10 ppm or less. Embodiments of the invention may includethree-dimensional parts formed according to any of the above methods.

These and other objects, along with advantages and features of thepresent invention herein disclosed, will become more apparent throughreference to the following description, the accompanying drawings, andthe claims. Furthermore, it is to be understood that the features of thevarious embodiments described herein are not mutually exclusive and mayexist in various combinations and permutations. As used herein, theterms “approximately” and “substantially” mean ±10%, and in someembodiments, ±5%. The term “consists essentially of” means excludingother materials that contribute to function, unless otherwise definedherein. Nonetheless, such other materials may be present, collectivelyor individually, in trace amounts. For example, a structure consistingessentially of multiple metals will generally include only those metalsand only unintentional impurities (which may be metallic ornon-metallic) that may be detectable via chemical analysis but do notcontribute to function. As used herein, “consisting essentially of atleast one metal” refers to a metal or a mixture of two or more metalsbut not compounds between a metal and a non-metallic element or chemicalspecies such as oxygen, silicon, or nitrogen (e.g., metal nitrides,metal silicides, or metal oxides); such non-metallic elements orchemical species may be present, collectively or individually, in traceamounts, e.g., as impurities.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIG. 1 is a schematic cross-sectional view of a plasma densificationapparatus utilized to form spherical powder particles in accordance withvarious embodiments of the invention;

FIG. 2A is a schematic cross-section of a wire preform in accordancewith various embodiments of the invention;

FIG. 2B is a schematic view of a wire being fabricated from a wirepreform in accordance with various embodiments of the invention;

FIG. 2C is a schematic cross-section of a wire preform containingmultiple coaxial tubes in accordance with various embodiments of theinvention;

FIG. 3 is a schematic of an additive-manufacturing apparatus utilized tofabricate three-dimensional metallic parts in accordance with variousembodiments of the invention;

FIG. 4A is an axial cross-section of a wire fabricated in accordancewith various embodiments of the invention;

FIG. 4B is a longitudinal cross-section of the wire of FIG. 4A;

FIG. 5 is a cross-sectional micrograph of a melted and resolidifiedmulti-principal element alloy wire fabricated in accordance with variousembodiments of the invention; and

FIGS. 6 and 7 are cross-sectional micrographs of a melted andresolidified high-entropy alloy fabricated in accordance with variousembodiments of the invention.

DETAILED DESCRIPTION

In various embodiments of the present invention, a preform in the shapeof, e.g., a rod or a bar, is provided by pressing and/or sintering acollection of powders. Collectively, the powders contain all of theelements of a desired HEA or MPEA. For example, one or more, or evenall, of the powders may each be composed of particles that include,consist essentially of, or consist of one of the alloy's constituentelements. In other embodiments, one or more of the powders may each becomposed of agglomerate particles including, consisting essentially of,or consisting of a mixture or alloy of two or more of the alloy'sconstituent elements.

In accordance with various embodiments of the invention, the preformcontains one or more powders composed of substantially sphericalparticles and one or more powders composed of non-spherical (e.g.,flaky, angular, irregular, etc.) particles. For example, powderparticles of tungsten and/or molybdenum (e.g., particles initiallyfabricated via a hydride/dehydride process or other process) may beplasma densified and may therefore be substantially spherical. Anexemplary apparatus 100 for plasma densification is shown schematicallyin FIG. 1. As shown, powder particles 110 may be loaded into a powderfeeder 120, which feeds the particles 110 through a plasma jet 130formed by, for example, a time-varying current applied to an inductioncoil 140 sparking a plasma 150 from plasma gas 160 fed into the coil140. The plasma jet 130 at least partially melts the particles 110,which subsequently resolidify into higher-density particles 170collected below the plasma 150. The plasma-densified particles 170 aregenerally substantially spherical due to the plasma-induced melting andminimization of surface area resulting during resolidification. Theminimization of the surface area of the particles also minimizes orsubstantially reduces the uptake of oxygen or other volatile species,and the plasma densification process itself volatilizes such species aswell, thereby reducing the concentration of such contaminants within thepowder 170. The plasma-densified powder particles 170 may have anaverage particle size of, for example, 15 μm to 45 μm, or even smaller.

FIG. 2A depicts the fabrication of a wire preform 200 in accordance withembodiments of the present invention. One or more types of substantiallyspherical powder particles 170 are mixed with one or more powders ofnon-spherical particles 210 (e.g., within a tube 220 or in a cylindricalmold) such that all of the elements of the desired alloy are includedwithin the preform 200. The non-spherical powder particles 210 may beformed by, e.g., a hydride/dehydride process. In various embodiments ofthe invention, the non-spherical powder particles are not rounded,oblong, ellipsoidal, and/or do not have smooth rounded surfaces alongany portion of their surface areas. The non-spherical powder particles210 may have an average particle size of, for example, less than orequal to 50 μm to 250 μm, or even larger. As mentioned above, either orboth of the substantially spherical particles 170 or the non-sphericalpowder particles 210 may be individually composed of an alloy or mixtureof two or more of the elements of the desired alloy. Such alloy powdersmay be formed via, e.g., hydride/dehydride of pre-alloyed ingots andoptional plasma densification of powders resulting therefrom.

In various embodiments, the melting point of one or more of the types ofsubstantially spherical particles 170 is higher than the melting pointof one or more of the types of non-spherical particles 210. In variousembodiments, the ductility of one or more of the types of substantiallyspherical particles 170 is lower than the ductility of one or more ofthe types of non-spherical particles 210. In various embodiments, noneof the metallic elements within the substantially spherical particles170 are present within the non-spherical particles 210 and vice versa.In various embodiments, one or more of the metallic elements of thedesired HEA are represented in both the substantially sphericalparticles 170 and the non-spherical particles 210. In some embodiments,both the substantially spherical particles 170 and the non-sphericalparticles 210 contain all of the metallic elements of the desired alloy,as elemental powder particles and/or alloy powder particles.

The resulting mixture of substantially spherical particles 170 andnon-spherical powder particles 210 within the preform 200 advantageouslyreduces or minimizes the amount of empty void space within the preform200. The particles 170, 210 are preferably distributed within thepreform 200 such that the composition of the preform 200 issubstantially homogeneous along its length. In various embodiments, thepreform 200 and/or at least a portion of the powder mixture therein maybe further densified before further processing into wire. For example,the preform 200 and/or the powder mixture may be pressed by, e.g., hotisostatic pressing or cold isostatic pressing. The powder or the preformmay be densified before and/or after inclusion of a sacrificial tube (asdetailed below). After formation of the preform 200, the preform 200 isprocessed into a wire 230. In an exemplary embodiment depicted in FIG.2B, the preform 200 is formed into wire 230 via drawing through one ormore drawing dies 240 until the diameter of the wire 230 is reduced tothe desired dimension. In various embodiments, various types of theparticles of the preform 200, particularly those having relatively lowductility (e.g., molybdenum, tungsten, etc.) may have their morphologiesdeform during the processing of the preform 200 into wire 230. Forexample, substantially spherical particles 170 of molybdenum and/ortungsten may be elongated into oblong shapes or ribbons (e.g., along thewire axis), and/or they may remain substantially spherical in the finalwire 230. Other types of particles having higher ductility (e.g.,tantalum, niobium, etc.) may elongate around the other particles andform a matrix disposed around the harder particles in the final wire. Invarious embodiments, the drawing is supplemented with or replaced by oneor more other mechanical deformation processes that reduce the diameter(or other lateral dimension) of the preform 200, e.g., pilgering,rolling, swaging, extrusion, etc. The preform 200 and/or wire 230 may beannealed during and/or after diameter reduction (e.g., drawing).

In various embodiments, the preform 200 is formed via the combination ofone or more substantially spherical powders 170 with one or morenon-spherical powders 210 within a tube 220 that includes, consistsessentially of, or consists of one or more of the elements of thedesired HEA or MPEA. The tube 220 may itself be coaxially disposedwithin one or more other tubes 250 that include, consist essentially of,or consist of one or more other elements of the HEA, as shown in FIG.2C. In such embodiments, the powders disposed within the tubes need notinclude the elements represented within the tube(s). When the preform200 containing the one or more tubes is drawn down into wire 230, thecross-section of the wire 230 will thus include all of the elementalconstituents of the desired alloy. In various embodiments, at least aportion of the powder mixture may be further densified before beingplaced into tube 220. For example, the powder mixture may be pressed by,e.g., hot isostatic pressing or cold isostatic pressing.

In various embodiments, the one or more tubes may include, consistessentially of, or consist of one or more elements that are more ductilethan one or more of the elements present in powder form. For example,the one or more tubes may include, consist essentially of, or consist ofNb, Ta, Ti, and/or Zr. In various embodiments, the one or more tubeshave a sufficiently small diameter that the preform 200 itself may beutilized as the final wire 230 without further processing or diameterreduction such as wire drawing. In various embodiments, the one or moretubes, with the powders therewithin, may be annealed and/or subjected topressure (e.g., hot-isostatically pressed) before (or between multiplesteps of) the process of diameter reduction. Such treatment mayadvantageously reduce void space within and increase the density of thefinal wire 230.

In various embodiments, the melting point of one or more of the types ofsubstantially spherical particles 170 and/or one or more of the types ofnon-spherical particles 210 is higher than the melting point of one ormore of the metallic elements of one or more of the tubes 220, 250. Invarious embodiments, the ductility of one or more of the types ofsubstantially spherical particles 170 and/or one or more of the types ofnon-spherical particles 210 is lower than the ductility of one or moreof the metallic elements of one or more of the tubes 220, 250. Invarious embodiments, none of the metallic elements within thesubstantially spherical particles 170 and/or the non-spherical particles210 are present within the tubes 220, 250 and vice versa. In variousembodiments, one or more of the metallic elements of the desired alloyare represented in at least one of the types of substantially sphericalparticles 170 and/or at least one of the types of non-sphericalparticles 210, as well as in one or more of the tubes 220, 250.

In other embodiments, the preform 200 may include, consist essentiallyof, or consist of a sacrificial tube 220 in which the various powders170, 210 are disposed. After processing of the preform 200 into wire230, the sacrificial tube 220 may be etched or melted away, and thefinal wire 230 includes, consists essentially of, or consists of theelements of the desired alloy arising solely from the original powders170, 210. In various embodiments, one or more tubes to be processed aspart of the wire may be disposed within the sacrificial tube 220; atleast portions of such tubes will typically remain as portions of thewire after removal of the sacrificial tube 220. The sacrificial tube 220may include, consist essentially of, or consist of, for example,plastic, rubber, one or more polymeric materials, a metallic materialhaving a melting point lower than one or more (or even all) of themetallic elements within the powders 170, 210, a metallic materialselectively etchable (i.e., over the metallic elements within thepowders 170, 210 and other tubes), etc.

Once wire 230 including, consisting essentially of, or consisting of theelemental constituents of a desired HEA or MPEA is fabricated inaccordance with embodiments of the invention, the wire 230 may beutilized to fabricate a three-dimensional part with an additivemanufacturing assembly 300. For example, as shown in FIG. 3, the wire230 may be incrementally fed, using a wire feeder 310, into the path ofa high-energy source 320 (e.g., an electron beam or a laser beam emittedby a laser or electron-beam source 330), which melts the tip of the wire230 to form a small molten pool (or “bead” or “puddle”) 340. The entireassembly 300 may be disposed within a vacuum chamber to prevent orsubstantially reduce contamination from the ambient environment.

Relative movement between a substrate 350 (which may be, as shown,disposed on a platform 360) supporting the deposit and the wire/gunassembly results in the part being fabricated in a layer-by-layerfashion. Such relative motion results in the continuous formation of alayer 370 of the three-dimensional object from continuous formation ofmolten pool 340 at the tip of the wire 230. As shown in FIG. 3, all or aportion of layer 370 may be formed over one or more previously formedlayers 380. The relative movement (i.e., movement of the platform 360,the wire/gun assembly, or both) may be controlled by a computer-basedcontroller 380 based on electronically stored representations of thepart to be fabricated. For example, the two-dimensional layers tracedout by the melting wire may be extracted from a stored three-dimensionalrepresentation of the final part stored in a memory 390.

The computer-based control system (or “controller”) 380 in accordancewith embodiments of the present invention may include or consistessentially of a general-purpose computing device in the form of acomputer including a processing unit (or “computer processor”) 392, thesystem memory 390, and a system bus 394 that couples various systemcomponents including the system memory 390 to the processing unit 392.Computers typically include a variety of computer-readable media thatcan form part of the system memory 390 and be read by the processingunit 392. By way of example, and not limitation, computer readable mediamay include computer storage media and/or communication media. Thesystem memory 390 may include computer storage media in the form ofvolatile and/or nonvolatile memory such as read only memory (ROM) andrandom access memory (RAM). A basic input/output system (BIOS),containing the basic routines that help to transfer information betweenelements, such as during start-up, is typically stored in ROM. RAMtypically contains data and/or program modules that are immediatelyaccessible to and/or presently being operated on by processing unit 392.The data or program modules may include an operating system, applicationprograms, other program modules, and program data. The operating systemmay be or include a variety of operating systems such as MicrosoftWINDOWS operating system, the Unix operating system, the Linux operatingsystem, the Xenix operating system, the IBM AIX operating system, theHewlett Packard UX operating system, the Novell NETWARE operatingsystem, the Sun Microsystems SOLARIS operating system, the OS/2operating system, the BeOS operating system, the MACINTOSH operatingsystem, the APACHE operating system, an OPENSTEP operating system oranother operating system of platform.

Any suitable programming language may be used to implement without undueexperimentation the functions described herein. Illustratively, theprogramming language used may include assembly language, Ada, APL,Basic, C, C++, C*, COBOL, dBase, Forth, FORTRAN, Java, Modula-2, Pascal,Prolog, Python, REXX, and/or JavaScript for example. Further, it is notnecessary that a single type of instruction or programming language beutilized in conjunction with the operation of systems and techniques ofthe invention. Rather, any number of different programming languages maybe utilized as is necessary or desirable.

The computing environment may also include other removable/nonremovable,volatile/nonvolatile computer storage media. For example, a hard diskdrive may read or write to nonremovable, nonvolatile magnetic media. Amagnetic disk drive may read from or writes to a removable, nonvolatilemagnetic disk, and an optical disk drive may read from or write to aremovable, nonvolatile optical disk such as a CD-ROM or other opticalmedia. Other removable/nonremovable, volatile/nonvolatile computerstorage media that can be used in the exemplary operating environmentinclude, but are not limited to, magnetic tape cassettes, flash memorycards, digital versatile disks, digital video tape, solid state RAM,solid state ROM, and the like. The storage media are typically connectedto the system bus through a removable or non-removable memory interface.

The processing unit 392 that executes commands and instructions may be ageneral-purpose computer processor, but may utilize any of a widevariety of other technologies including special-purpose hardware, amicrocomputer, mini-computer, mainframe computer, programmedmicro-processor, micro-controller, peripheral integrated circuitelement, a CSIC (Customer Specific Integrated Circuit), ASIC(Application Specific Integrated Circuit), a logic circuit, a digitalsignal processor, a programmable logic device such as an FPGA (FieldProgrammable Gate Array), PLD (Programmable Logic Device), PLA(Programmable Logic Array), RFID processor, smart chip, or any otherdevice or arrangement of devices that is capable of implementing thesteps of the processes of embodiments of the invention.

Advantageously, wires in accordance with embodiments of the inventionare substantially homogeneous in composition. Thus, all of the elementsof the desired HEA or MPEA are present in each small molten pool 340 ofmaterial at any particular instant during fabrication. Due to theirsmall size, the pools 340 cool quickly, locking in the desired alloycomposition. In addition, since empty void space within the wire 230fabricated in accordance with embodiments of the present invention wassubstantially eliminated via packing of powder particles with multipledifferent shapes and/or sizes, the wire 230 melts during additivemanufacturing with little if any sparking and without introducingporosity, cracks, or other defects into the printed part. After theadditive manufacturing process is complete, the part may be removed fromthe platform and subjected to final machining and/or polishing.

EXAMPLE

A substantially pure Cu tube having a 0.648 inch outer diameter and a0.524 inch inner diameter was wrapped around a Ta-3W (i.e., Ta—W alloycontaining approximately 3% W) welded tube having an outer diameter of0.500 inch and an inner diameter of 0.470 inch. A powder blend of 4weight percent Ta non-spherical powder particles, 32 weight percent Nbnon-spherical powder particles, 32 weight percent Mo substantiallyspherical powder particles, and 32 weight percent W substantiallyspherical powder particles was utilized to fill the Ta-3W tube at anapparent fill density of approximately 51%. The Ta and Nb powderparticles were low-oxygen powder particles formed by a hydride-dehydrideprocess and thus had the form of angular flakes. The Mo and W powderparticles were formed via a plasma densification process. Taking intoaccount the Ta-3W tube, the preform within the Cu tube contained 24.3atomic percent Ta, 25.7 atomic percent W, 25.0 atomic percent Mo, and25.0 atomic percent Nb. In total, 390 grams of powder were utilized.

The ends of the Cu tube were sealed with Cu plugs, and the assembly wascold swaged to 0.069 inch diameter in about 20 steps ranging from 5% to25% area reduction per pass, depending upon the available swage diameterfor each pass. To minimize powder slip within the tube, the rod wasswaged along one-half of its length, flipped, and then swaged from theopposite end until the whole assembly had a substantially uniformdiameter. Including the Cu tube and plugs, the starting weight was about935 grams, and the assembly produced more than 600 linear inches of wire(approximately 100:1 total area reduction). FIGS. 4A and 4B are,respectively, axial and longitudinal cross-sectional micrographs of thewire at a diameter of 0.084 inch. As shown, some of the initiallysubstantially spherical powder particles remain substantially spherical,while others have elongated along the long axis of the wire due to themechanical deformation. In general, the softer Ta and Nb powderparticles have elongated around the harder Mo and W powder particles.

The Cu-sheathed wire was continuous and could be coiled to a diameter of13 inches without breaking. The Cu sheath was removed prior to testing.For testing, lengths of the wire each having a length of 3 inches werecut and acid etched in a mixture of 25% nitric acid and 75% distilledwater until all of the Cu was removed. In order to simulate thehigh-speed melting and resolidification of an additive manufacturingprocess, wire sections totaling 32 grams in weight were placed in a coldCu hearth, and an electric arc from a W electrode supplied sufficientenergy to melt the wire. The Cu hearth rapidly cooled the metal, therebyclosely approximating the high rate of cooling in additivemanufacturing. A second set of samples included sufficient pure V addedto the hearth to produce a 20%-20%-20%-20%-20% (atomic percent) HEA ofV—Nb—Ta—Mo—W. This second set of samples could also have been producedvia inclusion of the proper amount of substantially spherical ornon-spherical V powder particles within the starting Ta-3W tube. All ofthe samples produced in accordance with this example melted readily intoa substantially homogenous mixture of their constituent elements andresolidified as a single solid solution phase. Moreover, all of thesamples melted very gently and quietly (i.e., with minimal or nosplattering, spitting, etc.), despite their origins as powder blends;thus, embodiments of the present invention have sufficiently highdensity and sufficiently low concentrations of volatile contaminants toensure compatibility with additive manufacturing, welding, and otherrapid melting and solidification processes.

Scanning electron microscopy (SEM) energy dispersive X-ray spectrometry(EDS) was performed on one of the second set of samples, and the averagecomposition of the five-element HEA was (22.6%-26.1%) W, (18.8%-20.6%)Ta, (18.8%-19.3%) Mo, (14.8%-16.0%) Nb, and (19.7%-23.3%) V, where allcompositions are atomic percentages. Via SEM analysis, the samples weredetermined to be single-phase with the expected dendriticmicrostructure, and the inter-dendrite spacing ranged from approximately10 μm to approximately 20 μm. FIG. 5 is a cross-sectional micrograph ofone of the first set of samples after melting and resolidification. Thesample was chemically etched to reveal the internal structure. As shown,some grain structure is visible with internal dendritic structure. Thesample was swab-etched (as opposed to being fully immersed) with anetchant prepared from 5 ml lactic acid, 5 ml hydrogen peroxide, 2 mlhydrofluoric acid, and 2 ml nitric acid. FIGS. 6 and 7 arecross-sectional micrographs of one of the second set of samples aftermelting and resolidification. The sample in FIG. 6 was also chemicallyetched (with the same etchant detailed above with reference to FIG. 5)to reveal the internal structure, and the sample in FIG. 7 was polishedbut not chemically etched. The dendritic microstructure of the sample isquite evident.

Finally, multiple Vickers hardness tests using a 1 kg load wereperformed on the first and second sets of samples, and the resultsobtained are included in the table below.

Hardness Hardness Hardness Composition (Test 1) (Test 2) (Test 3)Nb—Ta—Mo—W 490 533 524 V—Nb—Ta—Mo—W 561 579 591As expected, the second set of samples exhibits larger hardness valuesdue to the addition of V into the alloy. The hardness values for bothsets of samples are fairly high and imply high tensile strength of wiresfabricated in accordance with embodiments of the present invention.

The terms and expressions employed herein are used as terms andexpressions of description and not of limitation, and there is nointention, in the use of such terms and expressions, of excluding anyequivalents of the features shown and described or portions thereof. Inaddition, having described certain embodiments of the invention, it willbe apparent to those of ordinary skill in the art that other embodimentsincorporating the concepts disclosed herein may be used withoutdeparting from the spirit and scope of the invention. Accordingly, thedescribed embodiments are to be considered in all respects as onlyillustrative and not restrictive.

What is claimed is:
 1. A method of fabricating a metallic wire, themethod comprising: combining, to form at least a portion of a preform,(i) one or more first metal powders each comprising a plurality ofsubstantially spherical particles, and (ii) one or more second metalpowders each comprising a plurality of non-spherical particles, the oneor more second metal powders being mixed with the one or more firstmetal powders such that a composition of the preform is substantiallyhomogeneous along a length of the preform; and reducing a diameter ofthe preform via one or more mechanical deformation processes, therebyforming a metallic wire, wherein (i) the metallic wire comprises ahigh-entropy alloy comprising five or more metallic elements or amulti-principal element alloy comprising four or more metallic elements,(ii) each first metal powder comprises at least one of the metallicelements, (iii) each second metal powder comprises at least one of themetallic elements, (iv) the substantially spherical particles arespherical to within ±10% in any direction such that an eccentricity inany direction does not exceed 10%, and (v) the non-spherical particles(a) are elongated with an aspect ratio of at least 2:1, (b) areacicular, (c) have at least one flat surface, (d) are flakes, (e) haveat least one corner or vertex, or (f) are polyhedral.
 2. The method ofclaim 1, wherein the metallic elements comprise at least four of Nb, Ta,Mo, W, Ti, Hf, V, Zr, Al, or Cr.
 3. The method of claim 1, wherein thenon-spherical particles of at least one second metal powder are angularflakes.
 4. The method of claim 1, wherein the one or more mechanicaldeformation processes comprise at least one of drawing, pilgering,swaging, extrusion, or rolling.
 5. The method of claim 1, wherein thepreform comprises one or more metallic tubes surrounding the one or morefirst metal powders and the one or more second metal powders, eachmetallic tube comprising at least one of the metallic elements.
 6. Themethod of claim 1, wherein the one or more first metal powders and theone or more second metal powders are combined within one or moresacrificial tubes, and further comprising removing the one or moresacrificial tubes after reducing the diameter of the preform.
 7. Themethod of claim 1, wherein at least one said first metal powder isprovided by a process comprising: providing a plurality of metalparticulates; feeding the metal particulates into a plasma, thereby atleast partially melting the metal particulates; and cooling the at leastpartially melted metal particulates to form substantially sphericalparticles.
 8. The method of claim 1, wherein at least one said secondmetal powder is provided by a process comprising: hydrogenating metal toform a metal hydride; mechanically grinding the metal hydride into aplurality of non-spherical particles; and dehydrogenating thenon-spherical metal hydride particles.
 9. The method of claim 1, whereinat least one first metal powder is an elemental powder consistingessentially of one of the metallic elements.
 10. The method of claim 1,wherein at least one first metal powder is an alloy powder consistingessentially of two or more of the metallic elements.
 11. The method ofclaim 1, wherein at least one second metal powder is an elemental powderconsisting essentially of one of the metallic elements.
 12. The methodof claim 1, wherein at least one second metal powder is an alloy powderconsisting essentially of two or more of the metallic elements.
 13. Themethod of claim 1, wherein an oxygen concentration of the one or morefirst metal powders is 300 ppm or less.
 14. The method of claim 1,wherein an oxygen concentration of the one or more second metal powdersis 300 ppm or less.
 15. The method of claim 1, wherein an averageparticle size of at least one of the first metal powders ranges fromapproximately 15 μm to approximately 45 μm.
 16. The method of claim 1,wherein an average particle size of at least one of the second metalpowders is greater than approximately 50 μm.
 17. The method of claim 6,wherein removing the one or more sacrificial tubes comprises at leastone of melting or etching.
 18. The method of claim 1, furthercomprising: translating a tip of the wire relative to a platform;thereduring, melting a tip of the wire with an energy source to form amolten bead comprising the metallic elements, whereby the bead cools toform at least a portion of a layer of a three-dimensional part; andrepeating the above steps one or more times to produce thethree-dimensional part, wherein the three-dimensional part comprises thehigh-entropy alloy or the multi-principal element alloy.